The invention relates to a non-powered web stabilization apparatus in which an airfoil is specifically configured to utilize the boundary layer air associated with a moving web to stabilize the web and to assist changes to the web path as desired with minimal friction and without the use of externally supplied air.
In the manufacture of tissue (light weight, porous paper), there generally is a spacial separation (draw) between the exit from the dryer section of the paper machine, such as the Yankee cylinder dryer, and the winder area where the paper is wound into rolls for subsequent further processing at some location typically remote to the paper manufacturing machinery. This spacial separation provides isolation of the winder from the paper machine, while accommodating intermediate operations such as calendaring (bulk uniformity control), slitting (cutting the "as manufactured" paper width into multiple narrower widths), caliper control (real time measurement and adjustment of paper unit weight and/or moisture), and repulping (gathering, shredding and reconstituting as recycled pulp) that paper which is not being wound, such as at start-up or at a web break. Each of these intermediate operations has a stabilizing effect on the web, while at the same time may place special requirements on the position and steadiness of the web. Since these devices may or may not be continuously in use, a means must be provided in the web path to compensate for the non-use condition.
Historically, various means have been employed to control the web as it passes from the paper machine dryer section to the winder. These include bowed pipes or rolls, straight pipes or rolls, and large flat plates or other similar devices. The nature of tissue is such that it has substantial bulk with the surface being comprised to a multitude of pulp fibers radiating outwardly. These fibers are readily broken by firm contact with stationary rigid devices such as rolls or pipes, resulting in the production of an extremely fine paper dust which presents both a fire hazard situation, as well as a health hazard for the workers through ingestion into the lungs. The quantity of this dust present in the work-place air is now subject to Federal and State regulation, and its generation is an issue of concern. Ideally, physical contact with the virgin web should be avoided entirely, but this is neither practical or possible.
The most popular means of changing the web path through the tissue manufacturing process is the rigid pipe, whether bowed or straight, due to its simplicity and minimum cost. The pipe method has three major problems inherent in its use. The first is that the web is in firm contact with the pipe, thus requiring additional tension to be applied to the web. Secondly, since paper is abrasive (even soft, delicate tissue) the pipe will become worn and require replacement periodically. Thirdly, once the web is in contact with the pipe, it wants to remain attached to the curved surface of the pipe, thus requiring additional tension to break the web loose. Typically, dust particles will collect near the breakaway point, forming an extension of the pipe which eventually breaks off, falling onto the web and either contaminating the web or breaking it. The simple rigid pipe is effective in controlling the web and reducing web vibrations, although it does require frequent cleaning and periodic replacement.
Another popular web stabilizer and web transport system is the large flat plate style. These plates are typically several feet in machine direction length and are effective at holding webs which are subject to very strong air currents such as those emitted from the broke pit of the repulper system. Since this large flat plate generally occupies the majority of the draw between the dryer cylinder and the next machine element, it must be moved at time of start-up or web break to provide an unobstructed path for the web traverse to the repulper system broke pit. Movement of this plate requires the use of a mechanically driven member which adds to the total system complexity. The flat plate style exhibits two problems which are detrimental. First, the machine direction length is such that the web can alternately collapse against the surface of the plate, then pick up from the plate and subsequently collapse again (flutter), resulting in the generation of dust due to physical contact which in turn adds to the total web tension. Also, to provide sufficient structural rigidity, the plate must be made with some finite thickness to accommodate the inclusion of internal structural reenforcement. As a result of this thickness, the entry and exit ends are shaped (generally rounded) to facilitate smooth entry and exit. The behavior of these curved ends is similar to that of the rigid pipe design, except that the tendency for web attachment to the adjacent surface is more aggressive because the radius employed is greater than that of the typical rigid pipe.
Accordingly, it is an object of the invention to provide a non-powered web stabilization apparatus to overcome the aforementioned deficiencies in conventional devices.